1. Field of the Invention
The present invention relates generally to rejection systems, and more particularly to rejection systems for use with a product inspection system that are used to reject, for example, faulty products during product inspections.
2. Description of the Prior Art
In order to reduce labour costs, automation or an ultimate "no man" status at the inspection processes of products or the like, various types of automatic inspection systems that judge whether products are good or bad by using image sensors or the like, and then by processing electrical signals from the image sensors have been proposed, to replace the conventional human dependent visual inspection to check shape, colour, flaws, dirt, etc. of products.
Normally, since such objects being inspected are moving at high speeds on belt conveyers or the like, such inspection systems must positively judge whether the objects are good or bad while they are moving at high speeds within a short period of time. At the same time, when a bad product is discovered by the inspection system among the products that are flowing at high speeds on a conveyer, a rejection system must be driven by the rejection signal that is generated from the inspection system, to reject the bad product from the conveyer belt at a proper location. The bad product that is rejected from the conveyer by such rejection system is placed into an accumulation bucket or shifted onto another bad product transfer conveyer. As the belt conveyer flow speed is increased to higher speeds, the quantity of the objects to be inspected that flow within a given period of time increases so that the demand increases for the inspection system to have a corresponding inspection capability, along with the rejection capability of the rejection system to surely reject the bad products in compliance with the reject signals that are produced from the inspection system.
As for the inspection capabilities of the inspection system, since the new types of electronic circuitries are mainly used, it is relatively easy to shorten the inspection processing time. However, it would be meaningless, if the bad product rejection system that is to function by receiving the reject signals as delivered from the inspection system cannot surely follow up such signals even though the inspection capability of the inspection system is increased by shortening the inspection processing time.
The methods of rejection that are conventionally used to reject bad products depend upon suction or jet of air, or direct push out of the rejects, or changing the flow direction of the bad product by valves, etc. In such cases, the majority depends upon solenoids that use electro magnetic force to drive the bad product rejection mechanisms. For instance, for bad product rejection by air jet, a solenoid valve is used for pneumatic control, or otherwise, for the direct bad product rejection mechanism drives, magnetic solenoids of the types having plunger or rotary solenoids are used. Such magnetic solenoids require about 0.1-0.2 seconds of function time normally when in operation under load. If this function time is converted to the number of operations per minute, 600 to 300 are obtained. In other words, no matter how short the inspection processing time of the inspection system may be, the bad product rejection capabilities of the rejection systems limit the maximum product speeds to around 300 to 600 pieces per minute.
Generally, it is difficult to shorten the function time of magnetic solenoids, and although improvements are made, it is impossible to drastically shorten the function time.